cable problems, ground hums, resets


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Old 04-15-20, 07:50 AM
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cable problems, ground hums, resets

Hello folks, I am brand new to the forums. I am retired. My background includes some electronics, industrial maintenance mechanics, some automotive mechanics, and general tinkering.

I build vacuum tube stereo amplifiers and preamps as a hobby. I have about 18 months of formal electronic training(as opposed to an electrician) from about 40 years ago.

So to my question. I have a horrific ground hum in my stereo. I am 100% certain it is an induced voltage coming in on the shield of the comcast coaxialcable. I measure about 380mV from shield to a known solid ground. I am not sure what it should be. I have disconnected the cable at the house connection and it disappears. In other words, I have eliminated the possibility of the hum be created in the house. THe hum is a 60hz ground hum. If I ground the shield at the comcast box(tv box) the hum greatly reduces but does not disappear. Also, we are having huge amounts of connectivity issues with the interent, the phone and the tv. Our modem resets many times a day. Sometimes it is down for many hours.

Here is what I do know. The cable connecting my house is buried in a utlity easment in my yard. The main electrical supply for the neighborhood also goes through that easment. My assumption is the electrical lines are inducing a voltage into the cableshield.
THoughts?
 
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Old 04-15-20, 08:16 AM
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Is your cable grounded where it enters the house? Mine is about 6 feet away from my electric meter and the incoming cable is grounded to the house's electrical ground rods.
 
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Old 04-15-20, 09:29 AM
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Yep, grounded. I did try adding an additional ground on the shield right at the box(where it enterst the comcast dvr), and it did reduce the hum slightly, but it did not eliminate it.

I have done more testing, I am 100% certain it is a signal coming from the comcast line. I just had the comcast tech here. He tried a ton of things. Fianlly, I just had him run a new cable from the pillar to the house. We moveds the cable so as not to be in proximity to the HV line in the easement. The hum is not gone, but reduced by maybe 60-70%. The techs meter also showed a significant decrease in noise on the line. SO here is hoping!!!!!!!
 
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Old 04-15-20, 05:32 PM
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How does the cable signal get to your receiver ?
Do you have a cable box connected via RCA cables to your receiver ?
Is your receiver tubed ?
 
 

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